All of the default language support happens from your application's language dropdown menu when you create it in our Dev Hub. After the app is created you cannot change the default language of the app (though this can be overridden later in the API).

This default language works natively in the preview UI, so you'll see the concepts from the general model listed in that language. Autocomplete dropdown works in that language too, as does Search. All created concepts will be in your actual language (i.e. we won't magically translate your "name" of your concept, .so if your app is in Japanese and you create a custom concept "dog" it's going to be named "dog" and not the Japanese equivalent. Which is 犬 if anyone is curious). This is because it is assumed that if your default language is Japanese then you'd actually know and name your concept a Japanese name.